Method of bypassing vocoders in digital mobile communication system

ABSTRACT

A method of bypassing vocoders in a digital mobile communication system, comprising the step of appending bypass mode data to data transmitted from a plurality of mobile stations, the bypass mode data instructing the vocoders not to perform encoding/decoding operations, and the step of transmitting the resultant data. According to the present invention, the unnecessary encoding/decoding operations are omitted for a mobile to mobile communication. Therefore, the present invention has the effect of removing the delay time and enhancing the voice quality.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a digital mobilecommunication system employing a code division multiple access (referredto hereinafter as CDMA) manner, and more particularly to a method ofbypassing vocoders in the digital mobile communication system, in whicha CDMA controller bypasses a voice signal without encoding and decodingit for communication between mobile stations, so that the voice qualitycan be enhanced.

2. Description of the Prior Art

Generally, for a mobile to LAND communication, a CDMA controllerreceives encoded voice data from a mobile station and decodes thereceived data. Then, the CDMA controller modulates the decoded datausing a pulse code modulation (referred to hereinafter as PCM) mannerand transmits the resultant PCM data to a switching system.

On the other hand, for a mobile to mobile communication, a CDMAcontroller of one mobile station receives PCM data from the other mobilestation and encodes the received PCM data. Then, the CDMA controllertransmits the encoded data to the corresponding mobile station.

As seen from the above description, the CDMA controller performs theunnecessary decoding and encoding operations.

However, now, the CDMA controller must perform the decoding and encodingoperations for all communication processes. The decoding and encodingoperations may not be necessary to some communication processes. In thiscase, if the decoding and encoding operations are performed, they resultin an increase in delay time and a degradation in voice quality.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblem, and it is an object of the present invention to provide amethod of bypassing vocoders in a digital mobile communication system,in which the vocoders do not perform encoding and decoding operationswhen a communication line does not require the encoding and decodingoperations, so that the voice quality can be enhanced and the delay timecan be reduced.

The present invention is directed to a method of bypassing vocoders inMobile-to-Mobile Call (MMC). In the call establishment process of adigital mobile communication system, the Mobile Service Switching Center(MSC) usually decides if a call is a Mobile-to-Mobile call or aMobile-to-Land call. This operation of MSC is known in the art.

In accordance with the present invention, the above and other objectscan be accomplished by a provision of a method of bypassing vocoders ina digital mobile communication system, comprising the step of appendingbypass mode data to data transmitted from a plurality of mobilestations, the bypass mode data instructing the vocoders not to performencoding/decoding operations, and the step of transmitting the resultantdata.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of a signal transfer apparatus for embodying amethod of bypassing vocoders in a digital mobile communication systemusing packet routing dedicated communication ports in accordance with anembodiment of the present invention; and

FIG. 2 is a block diagram of a signal transfer apparatus for embodying amethod of bypassing vocoders in a digital mobile communication systemusing a vocoder control program in accordance with an alternativeembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a block diagram of a signal transferapparatus for embodying a method of bypassing vocoders in a digitalmobile communication system using packet routing dedicated communicationports in accordance with an embodiment of the present invention. Asshown in this drawing, the signal transfer apparatus comprises one basestation 2 for receiving signals from a plurality of mobile stations 1,and a first selector 3 included in one CDMA controller. The signaltransfer apparatus further comprises the other base station 2′ forreceiving signals from a plurality of mobile stations 1′, and a secondselector 3′ included in the other CDMA controller. The first selector 3includes a vocoder 3-1 for encoding/decoding a voice signal from thebase station 2, and packet routing dedicated communication ports 3-2 forbypassing the voice signal from the base station 2 directly to the otherCDMA controller without transferring it to the vocoder 3-1. The basestation 2′ and second selector 3′ are the same in construction andoperation as the base station 2 and first selector 3, respectively. Aplurality of signal transfer apparatus with the above-mentionedconstruction may be connected to every switching system, as well-knownin the art.

Now, the method of bypassing the vocoders in the digital mobilecommunication system using the signal transfer apparatus with theabove-mentioned construction in accordance with the embodiment of thepresent invention will be described in detail.

The base stations 2 and 2′ receive radio voice signals as encoded datawith appended bypass mode data from the plurality of mobile stations 1and 1′ subscribing thereto and transmit the received signals to the CDMAcontrollers, respectively.

The CDMA controllers process the received signals in such a manner aswill hereinafter be described in detail.

Data formats of the received signals are retrieved by the selectors 3and 3′ in the CDMA controllers and call control processors (not shown)therein which are connected to the packet routing dedicatedcommunication ports 3-2 and 3-2′, respectively. In accordance with theretrieved result, it is determined whether the received signals are tobe passed to the vocoders 3-1 and 3-1′ or to be bypassed.

Channels of the received signals are matched with those of the selectors3 and 3′. Then, signals to be bypassed are bypassed through the packetrouting dedicated communication ports 3-2 and 3-2′. In other words, theselectors and call control processors determine based on the dataformats whether the received signals are to be passed to the vocoders orto be bypassed.

The voice signals to the vocoders 3-1 and 3-1′ are encoded and decodedthereby and then transmitted to the CDMA controller of the other party.The bypassed voice signals are transmitted directly to the CDMAcontroller of the other party through the packet routing dedicatedcommunication ports 3-2 and 3-2′.

The transmission and reception operations of the first selector 3 in theCDMA controller will hereinafter be described to explain theabove-mentioned process in more detail.

First, the reception operation of the first selector 3 in the CDMAcontroller will hereinafter be described.

Encoded data from a selected one of the mobile stations 1 is transmittedto the first selector 3 through the base station 2. The transmitted datais not applied to the vocoder 3-1 but transferred to the second selector3′ in the CDMA controller of the other party through the packet routingdedicated communication ports 3-2.

Next, the transmission operation of the first selector 3 in the CDMAcontroller will hereinafter be described.

Bypassed data from the second selector 3′ in the CDMA controller of theother party is transmitted to the first selector 3. The transmitted datais temporarily stored in a buffer (not shown). Under this condition,when an interrupt signal TX TICK indicating a transmission time point ismade active, the stored data from the buffer is transmitted to aselected one of the mobile stations 1 through the base station 2. Thetransmission and reception operations of the second selector 3′ in theCDMA controller are performed in the same manner as those of the firstselector 3 and a description thereof will thus be omitted.

As mentioned above, the packet routing dedicated communication ports 3-2and 3-2′ are additionally installed on the existing hardware equipment.This has the effect of simplifying a software work. Also, theunnecessary work or the decoding and encoding operations in the CDMAcontroller are omitted, resulting in the improvement in voice quality.Further, the delay time resulting from the encoding operation can beshortened.

Referring to FIG. 2, there is shown a block diagram of a signal transferapparatus for embodying a method of bypassing vocoders in a digitalmobile communication system using a vocoder control program inaccordance with an alternative embodiment of the present invention. Asshown in this drawing, the signal transfer apparatus comprises one basestation 2 for receiving signals from a plurality of mobile stations 1,and a first selector 4 included in one CDMA controller. The signaltransfer apparatus further comprises the other base station 2′ forreceiving signals from a plurality of mobile stations 1′, and a secondselector 4′ included in the other CDMA controller. The first selector 4includes a vocoder 4-1 for encoding/decoding a voice signal from thebase station 2. The base station 2′ and second selector 4′ are the samein construction and operation as the base station 2 and first selector4, respectively.

Now, the method of bypassing the vocoders in the digital mobilecommunication system using the signal transfer apparatus with theabove-mentioned construction in accordance with the alternativeembodiment of the present invention will be described in detail.

To determine whether the present mode is a bypass mode or an existingmode, the selectors 4 and 4′ have frame pack and unpack functions forproducing a traffic data format of the bypass mode. The receivingselector converts the mode of its vocoder into the bypass mode. Here,all base stations and selectors can perform a bidirectionalcommunication. For this reason, the reference numerals for thediscrimination between transmitting and receiving selectors will beomitted.

The vocoder of bypass mode analyzes a PCM data format inputted therein,to determine whether the data frame is to be transmitted in the bypassmode. If it is determined that the data frame is to be transmitted inthe bypass mode, the vocoder sets its mode to the bypass mode and thentransmits the data.

Noticeably, a data rate must be changed to transmit a voice signal inthe bypass mode. To this end, data format conversion is performed tomatch a mobile station's data speed with a PCM data speed for thebypassing, as will hereinafter be mentioned in more detail.

The mobile station's data speed can be matched with the PCM data speedof 64 Kbps by repeating 22-byte data of the mobile station seven timesand adding a 6-byte header to the resultant data. That is,

22 bytes (mobile station's encoded data)·7+6=160 samples (bytes)/20 msec

where, 160 samples (bytes) indicate an amount of data stored in the unitof frame and 20 msec indicates a transmission time required in the unitof frame (i.e., 125 μsec (8 KHz)·160 samples).

The voice signal received in the bypass mode is directly converted intoPCM data for transmission without passing through decoding and encodingoperations. This has the effect of shortening the delay time resultingfrom the encoding operation, which is conventionally 47.5 msec in theunit of frame.

The conventional delay time is required in the following manner. Namely,a first data frame is received at a rate of 20 msec and then encoded. Asecond data frame is received at the moment that the encoded first dataframe is transmitted. A third data frame is received at the moment thatthe encoded second data frame is transmitted. In this manner, about 380samples are delayed for an interval of 47.5 msec.

The transmission and reception operations of the first selector 4 in theCDMA controller will hereinafter be described to explain theabove-mentioned process in more detail.

First, the reception operation of the first selector 4 in the CDMAcontroller will hereinafter be described.

Encoded data from a selected one of the mobile stations 1 is transmittedto the first selector 4 through the base station 2. In the firstselector 4, the vocoder 4-1 receives the encoded data. In the case wherethe received data is to be bypassed, the vocoder 4-1 performs nodecoding operation for the received data and changes only the data rateto transmit the received data to a PCM line.

Next, the transmission operation of the first selector 4 in the CDMAcontroller will hereinafter be described.

Bypassed data from the second selector 4′ in the CDMA controller of theother party is transmitted to the first selector 4. In the firstselector 4, the vocoder 4-1 receives the bypassed data and performs noencoding operation for the received data. The vocoder 4-1 then changesonly the data rate to transmit the received data to a selected one ofthe mobile stations 1 through the base station 2 when an interruptsignal TX TICK indicating a transmission time point is made active. Thetransmission and reception operations of the second selector 4′ in theCDMA controller are performed in the same manner as those of the firstselector 4 and a description thereof will thus be omitted.

As apparent from the above description, according to the presentinvention, the unnecessary encoding/decoding operations are omitted forthe mobile to mobile communication. Therefore, the present invention hasthe effect of removing the delay time and enhancing the voice quality.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A method of transmitting data in a digital mobile communication system employing vocoders, comprising the steps of: appending bypass mode data to encoded data transmitted from a plurality of mobile stations, said bypass mode data instructing a first vocoder to not decode the data and a second vocoder to not encode the data; and transmitting the resultant data.
 2. The method of claim 1, wherein each of said vocoders is adapted to set its mode to a bypass mode, to analyze a data format of an input signal to determine whether the input signal is to be bypassed, to change only a data rate only if it is determined that the input signal is to be bypassed and to transmit the bypassed input signal at the changed data rate.
 3. A method of transmitting data in a digital mobile communication system employing vocoders, comprising the steps of: appending bypass mode data to encoded data transmitted from a plurality of mobile stations, said bypass mode data instructing a first selector having a first vocoder and a second selector having a second vocoder whether to bypass the respective vocoders and transfer the data to packet routing dedicated communication ports; and transmitting the transferred data.
 4. The method of claim 2, wherein the data rate is changed by matching a mobile station's data speed with a PCM data speed.
 5. The method of claim 4, wherein the mobile station's data speed is matched with the PCM data speed of 64 Kbps by repeating 22-byte data of the mobile station seven times and adding a 6 -byte header to the resultant data.
 6. The method of claim 3, wherein said appending step includes a step of determining based on data format of said bypass mode data whether the transmitted encoded data are to be passed to the vocoders or to bypass the vocoders.
 7. The method of claim 6, wherein the determination of bypassing vocoders is made by call control processors which are connected to the packet routing dedicated communication ports. 